Two-stage turbo compressors for compressing a refrigerant in two stages are frequently employed as turbo compressors used in refrigerant compressors of turbo chillers. A two-stage turbo compressor is equipped with a first impeller and a second impeller disposed downstream of this first impeller.
Such two-stage turbo compressors include turbo compressors equipped with first inlet guide vanes and second inlet guide vanes at respective refrigerant inlets of each impeller (see Patent Document 1). Generally, the degree of opening of the second inlet guide vanes is made dependent on the degree of opening of the first inlet guide vanes by a link mechanism or the like, so as to be equal to the degree of opening of the first inlet guide vanes, or greater.
Patent Document 1:
Japanese Unexamined Patent Application, Publication No. 2003-307197 (paragraph [0025] and FIG. 2)